In providing insulating materials for wall space within the walls of residential and commercial buildings, and also the attic space of buildings, in the past it has been difficult to measure the actual amount of material delivered to the space. The insulating material is typically in fiber form and contained in bags at the time of delivery to the building site requiring insulation. Although one can be sure of the amount of material in a particular bag, verification of the amount actually sprayed into the wall or attic space, to insure that the consumer has obtained what he purchased, has been difficult at best. The problem in measuring the flow of such fibrous materials has been that the density can change. Although the volume flow can be measured, it is often difficult to relate volumetric flow rate to the actual quantity of fibrous material delivered to the wall since the density of the material can be varied significantly.
The invention described herein has overcome the problems in measuring fibrous material, and in particular, insulation used for insulating wall space. The invention relates to a system for accurately measuring the amount of fibrous material delivered by providing compensation for variation in density of the material as well as changes in volume flow rate. More specifically, the invention relates to the use of an acoustic signal generated in combination with an acoustical sensor and a comparator for comparing the signal generated with the signal received from the sensor to determine the amount of material in a given chamber. The acoustical generator such as a loudspeaker is placed at one end of a housing while the microphone or other acoustical sensing means is displaced relative to the loudspeaker at another portion of the housing so that chamber of material can pass between them. Chambers having insulating material for delivery to the wall space are them moved past the speaker and microphone assembly. The speaker is activated by a source signal to generate an acoustical signal to the successive chambers as they pass between the speaker and microphone. The microphone senses the acoustical wave generated as modified by the material in a given chamber and generates a corresponding electrical signal to a computer which then computes the relationship between the source signal and the sensed signal to produce a signal corresponding to the volume and density of material in the chamber. The computer can then sum the measurements for each chamber, such that a running tabulation of the amount of material being delivered can be obtained.
In another embodiment of the invention, the measuring apparatus simply measures the "R" factor rather than the quantity or density or some other parameter of material. The "R" factor is the insulating value of a given material. It has been learned that the "R" factor of a material is directly related to a sound attenuation. By applying this relationship to the audio measuring apparatus and other elements of the system, one can measure the "R" of a material being delivered to a cavity for insulation quite readily without resort to additional parameters such as the type of material employed and additional computations to adjust quantities to the alternate "R" factor which is typically the factor most desired.
It has been determined that different insulator materials attenuate sound at different rates. For example, rock wool is about 6.5 db/ounce, glass wool is about 12 db/ounce, and cellulose fiber is about 7.2 db/ounce. In checking the charts that all wool manufacturers are required to print on every bag of wool regarding the coverage or per square foot yield based on pounds, it has been computed that rock wool's typical "R" value per ounce is about 1.34. Glass wool is about 2.4 r/ounce and cellulose is about 1.42 r/ounce. That produces a direct relationship between db or audio attenuation and "R" factor for the material being measured. The advantage of using a system for simply measuring the "R" factor is that one need not make special consideration for different materials. Rather regardless of the material, their "R" value can be readily measured without adjustments in the system. The advantage of such a system is when the insulator appears at a location and must change the type of insulation employed. In other systems, this may create a problem requiring further computation. With the system using the relationship between audio attenuation and "R" factor, one can simply add new material in lieu of the old material and have the system continue to measure the "R" factor of the material being used as a fill for wall space or other area of a building.
Another advantage of having a metered system and particularly one which prints out the amount of "R" factor being delivered is that the opportunity for misrepresenting the amount of material delivered to a particular location is substantially impaired. Certain state authorities have been attempting to find ways to insure that insulators around the country are not misrepresenting the amount of insulation they deliver and thereby overcharge the customer. A fool proof or at least largely fool proof system has been sought to avoid fraud or other misuse to customers purchasing insulation. By using a system that simply measures the "R" factor, which avoids computation and a chance for misrepresentation, the customer can be assured that he has received the amount of material he has purchased. When a fool proof measuring system such as the one described herein is used, it becomes easier for inspection and other regulatory agencies to determine whether insulators or other vendors are delivering the requisite amounts of insulation.
In addition, by adopting the system that uses an audio frequency for measuring "R" factor, inspection of an in situ situation is made much easier. To measure the "R" factor of insulation in place, the cookie cutter approach typically has been used. This approach requires the operator to crawl between the joist in the flooring using instruments to cut through the wool or other insulating material and actually withdraw it from its in situ position for measuring. This system is cumbersome, dangerous to the operator and provides the opportunity for damage to the building if not conducted properly. By using a system that employs an acoustical mechanism and relates attenuation to the "R" factor, these problems can largely be overcome.
A system employing a sound attenuation can use a sound generator having a source which constantly produces the sound and a system which compensates for changes in the sound due to external factors. Another system which can be employed and one which eliminates a certain amount of electronics is the use of a pulse system in which a single pulse is generated over a given period of time.
With a pulse system an impulse generator is connected to an audio transducer to change the electrical signal to the audio signal used within the chamber. The attenuated audio signal is then transformed to an electrical signal, converted to a digital signal and delivered to a computer for additional computation. An LCD or printer is connected to the computer to permit a visual display of "R" value data corresponding to the signal sensed. The computer also controls the impulse generator and peak detector to insure they they are operated in the proper time sequence with regard to the chamber being measured. Various voltage converters can be employed to accommodate a fixed power source with the various elements in the system.
The advantage of this system is the avoidance of interference and other problems associated with other audio devices. The additional circuitry and other absorption systems as described above are simply not needed. Also by relating the output directly to "R" value, and the computer being properly programmed, the correct amount of insulation can be chosen for a given area. After delivery is completed a computer printout can be provided to the customer as a receipt verifying the amount actually delivered.
The above has been a general description of some of the problems which have been involved in measuring the delivery of fibrous materials and some advantages of the invention described herein. Other advantages will become apparent from the detailed description of the preferred embodiment which follows.